In, a 4-cycle 4-cylinder internal combustion engine for a vehicle, a secondary inertia force occurs at a center of gravity of a piston connecting rod system due to its layout.
As means for cancelling the secondary inertia force, the engine has a balancer apparatus for rotating balancer shafts at a speed that is twice as high as an engine rotational speed.
As a method of disposing the balancer apparatus, generally, there is a method whereby the balancer apparatus is integrated with a cylinder block or a method whereby the balancer apparatus is attached to a lower crank casing or an oil pan at a position just under a crank shaft.
In the case of the disposing method of attaching the balancer apparatus to the lower crank casing or the oil pan at the position just under the crank shaft, there is such a construction that the balancer shafts and the crank shaft are coupled by a chain. In the case of using the chain as mentioned above, it is indispensable to provide a chain tensioner.
Hitherto, as a driving apparatus of a balancer unit, JP-A-2000-9291 discloses an apparatus with a balancer apparatus arranged just under a crankshaft, a chain wound between a sprocket of the crank shaft and a sprocket of a balancer shaft of the balancer apparatus, and a cover provided in the oil pan for shutting off the sprocket of the crank shaft and a part of the chain from oil in the oil pan, thereby preventing an air-mixed oil from being sucked into an engine.
JP-A-2000-65145 discloses a balancer apparatus of a reciprocating piston engine, wherein the balancer apparatus is arranged just under a crank shaft, a chain is wound between a sprocket of a crank shaft and a sprocket of a balancer shaft of the balancer apparatus, a rotor of a lubricating oil pump is directly coupled with one of two balancer shafts, and a chain tensioner is arranged in an edge portion of the other balancer shaft, thereby miniaturizing the balancer apparatus.
Hitherto, a balancer apparatus of an engine having an oil pump is attached to the lower crank casing or the oil pan at a position just under the crank shaft. Since the balancer shafts and the crank shaft are coupled by the chain, there are such inconveniences in that the oil which has been stirred by the chain and in which the air has been mixed is liable to be sucked into the oil strainer and thus performance of the balancer apparatus deteriorates due to the layout or to the arrangement of the chain tensioner for applying tension to the chain.
Therefore, an object of the invention is to provide a balancer apparatus for an engine having an oil pump, wherein oil in which the air has been mixed is prevented from being sucked into the oil pump, and thus assembling performance of the balancer apparatus is improved.